Automatic control function programming manual ladder language

Storage of the reception buffer
@ Buffer start address
Written by the user
programme
Written by
the monitor
Programming error causing a CPU fault
Access to a prohibited address:
- &datagram parameter error,
- &datagram+size outside authorised area.
15.4.3 Programming Rules
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Buffer size
(1 word)
Request size
(1 word)
Answer
(see Sec. 15.3)
1 word
128 bytes
max.
For rational organisation of a programme including exchanges by protocol, follow the recommendations given below.
! CAUTION
Functions unito(), uniti(), neto() and neti() must be programmed in a background task
(%TF0 to %TF15).
The size of a request must not be zero or greater than 128 bytes (except for the READ_BLOCK and WRITE_BLOCK
requests).
REMARK Sixteen exchange buffers are accessible to the user programme, allowing a maximum
of sixteen requests to be sent each RTC cycle.
Consecutive transmission of several requests on the same port without acknowledgement of the answers causes the
loss of one or more answer codes.
It is important to:
- programme transmission to the server followed by reception of the answer on a given port before programming any
other transmission, or
- use different ports for each transmission/reception command.
For the servers, the concept of queuing may cause an offset in the timing of request processing. This is because the
load on the different servers may mean that the requests are not processed in the order in which they were sent.
To ensure correct timing of request processing, make sure the answer is received before sending the next request on
a port.
Buffer size